1. Field of the Invention
This invention relates to a telescopic swivel pipe joint for coupling a pair of axially spaced pipes to constitute, for example, a water supply line which does not break even in the event of earthquake or ground subsidence, and more particularly to an improved telescopic swivel pipe joint which is capable of providing ready adjustment in the degree of allowable telescopic swivel movement.
2. Description of the Prior Art
As is well known, pipe lines which are laid in the ground are often adversely affected by various factors. Most serious of these adverse factors are earthquake and ground subsidence because they can cause breakage of the pipe line.
To avoid or alleviate the adverse influences of earthquake and ground subsidence, West German patent publication No. 1039798 (Patented: Sept. 25, 1958; Inventors: Hans Kreidel, et al) proposes a swivel pipe joint which has such a construction as shown in FIG. 7 of the accompanying drawings.
Referring to FIG. 7, the swivel joint of the West German publication comprises a pair of joint sockets 100a, 100b respectively connected to a pair of pipe ends (not shown). Each joint socket 100a (100b) consists of two detachable parts 101a, 102a (101b, 102b) which, when assembled, internally provides a spherically concave bearing surface 103a (103b) to slidably support a spherical body 104a (104b).
The swivel joint further includes a pair of joint tubes 105a, 105b each screwed at one end thereof to a corresponding spherical body 104a (104b), so that the joint tube is swivelable or universally movable relative to the joint socket. The other end of each joint tube 105a (105b) is screwed to an intermediate tube 106 to make a non-expansible but adjustable connection to the other joint tube 105b (105a).
In application of the above described swivel joint, the overall length of the joint (the distance between the pair of joint sockets 100a, 100b) is adjusted by turning the intermediate tube 106 prior to laying down the joint in the ground. However, once adjusted and laid down in the ground, the swivel joint is no longer extensible nor compressible, so that the joint or the pipes connected thereto may break under tension and compression attendant with earthquake or ground subsidence. Further, the non-expansibility of the joint poses a vital limitation on the swivel movement of the joint which has been laid in the ground.
Japanese patent application laid-open No. 57-173683 (Laid-open: Oct. 26, 1982; Application No.: 56-58795; Filed: Apr. 18, 1981; Applicant: Kabushiki Kaisha Suiken, et al; Inventor: Toshiyuki SATO) discloses a telescopic swivel pipe joint which has overcome the disadvantages of the non-extensible swivel pipe and which is illustrated in FIGS. 8 and 9 of the accompanying drawings.
Referring to FIGS. 8 and 9, the telescopic swivel joint comprises a pair of spherical joint connectors 200a, 200b respectively connected to a pair of pipe ends 201a, 201b. The joint further includes a pair of joint tubes 202a, 202b each having a cylindrical portion 204a (204b) and a spherical socket portion 203a (203b) swivelably fitted on a corresponding joint connector 200a (200b). The cylindrical portion 204a of one joint tube 202a has a radially outward annular projection 205 and is slidably or telescopically fitted in the cylindrical portion 204b of the other joint tube 202b which is provided with a pair of radially inward annular projections 206, so that the two joint tubes are axially slidable within a limited stroke l relative to each other.
Because of the telescopic expansibility, the above joint ensures swivel movement of a maximum amplitude h (FIG. 9) which is determined by a maximum length L of the joint and the axial stroke l, thereby preventing breakage of or damage to the joint at the time of earthquake or ground subsidence.
When the ground in which the telescopic swivel joint is to be laid is weak, the maximum amplitude or allowable level deviation h of the joint must naturally be increased. In other words, the maximum amplitude h must be selected depending on particular ground conditions to constitute a pipe line which is most suited to such ground conditions.
Since the maximum amplitude h of the telescopic swivel joint is determined by the maximum length L and the axial stroke l as described before, it is necessary to replace at least one of the joint tubes 202a, 202b by another differently dimensioned joint tube. However, such replacement requires costly redesigning and manufacture of the new joint tube particularly due to the spherical socket portion (see 203a, 203b in FIG. 8) which necessitates precision to ensure smooth swivel movement.